package org.bouncycastle.crypto.paddings;

import java.security.SecureRandom;

import org.bouncycastle.crypto.InvalidCipherTextException;

/**
 * Block cipher padders are expected to conform to this interface
 */
public interface BlockCipherPadding {
    /**
     * Initialise the padder.
     * 
     * @param random
     *            the source of randomness for the padding, if required.
     */
    public void init(SecureRandom random) throws IllegalArgumentException;

    /**
     * Return the name of the algorithm the cipher implements.
     * 
     * @return the name of the algorithm the cipher implements.
     */
    public String getPaddingName();

    /**
     * add the pad bytes to the passed in block, returning the number of bytes
     * added.
     * <p>
     * Note: this assumes that the last block of plain text is always passed to
     * it inside in. i.e. if inOff is zero, indicating the entire block is to be
     * overwritten with padding the value of in should be the same as the last
     * block of plain text. The reason for this is that some modes such as
     * "trailing bit compliment" base the padding on the last byte of plain
     * text.
     * </p>
     */
    public int addPadding(byte[] in, int inOff);

    /**
     * return the number of pad bytes present in the block.
     * 
     * @exception InvalidCipherTextException
     *                if the padding is badly formed or invalid.
     */
    public int padCount(byte[] in) throws InvalidCipherTextException;
}
